首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   671篇
  免费   34篇
化学   433篇
晶体学   6篇
力学   24篇
数学   58篇
物理学   184篇
  2024年   2篇
  2023年   9篇
  2022年   13篇
  2021年   13篇
  2020年   16篇
  2019年   23篇
  2018年   18篇
  2017年   13篇
  2016年   25篇
  2015年   23篇
  2014年   30篇
  2013年   55篇
  2012年   52篇
  2011年   61篇
  2010年   22篇
  2009年   34篇
  2008年   30篇
  2007年   29篇
  2006年   15篇
  2005年   30篇
  2004年   30篇
  2003年   17篇
  2002年   22篇
  2001年   11篇
  2000年   12篇
  1999年   8篇
  1998年   9篇
  1997年   4篇
  1996年   3篇
  1995年   6篇
  1994年   7篇
  1993年   5篇
  1992年   3篇
  1990年   2篇
  1989年   2篇
  1986年   3篇
  1985年   3篇
  1984年   3篇
  1982年   5篇
  1981年   6篇
  1980年   6篇
  1979年   4篇
  1977年   2篇
  1976年   3篇
  1974年   2篇
  1973年   2篇
  1972年   2篇
  1971年   2篇
  1963年   1篇
  1961年   2篇
排序方式: 共有705条查询结果,搜索用时 31 毫秒
41.
We focus on the possible thermal channel of the well-known Lithosphere–Atmosphere–Ionosphere Coupling (LAIC) mechanism to identify the behavior of thermal anomalies during and prior to strong seismic events. For this, we investigate the variation of Surface Latent Heat Flux (SLHF) as resulting from satellite observables. We demonstrate a spatio-temporal variation in the SLHF before and after a set of strong seismic events occurred in Kathmandu, Nepal, and Kumamoto, Japan, having magnitudes of 7.8, 7.3, and 7.0, respectively. Before the studied earthquake cases, significant enhancements in the SLHF were identified near the epicenters. Additionally, in order to check whether critical dynamics, as the signature of a complex phenomenon such as earthquake preparation, are reflected in the SLHF data, we performed a criticality analysis using the natural time analysis method. The approach to criticality was detected within one week before each mainshock.  相似文献   
42.
43.
A cellulose derivative/liquid crystal composite‐type electro‐optical cell using a commercial cholesteric liquid crystal (CLC) was investigated. The electro‐optical properties of the system were examined, i.e. the dependence on applied voltage of the reflected wavelength and the minimum and maximum transmissions. A thin film of the CLC was dispersed with a cross‐linked cellulose film of 25 µm thickness. In the voltage dependence of the reflected wavelength it was verified that there is a hysteresis in the reflected wavelength. The variation of the reflected wavelength with temperature was also determined. The results are analysed in the framework of similar systems described in the literature for CLC dispersed in a polymer matrix.  相似文献   
44.
The aim of this study is to refine the understanding of the tribo-electrostatic phenomena that can affect the efficiency of suction-type dilute-phase transport systems. The study was conducted with mm-size ABS-PC particles, a granular material originating from genuine information technology wastes. The tribo-charging process was modelled using the response surface method of experimental design. The controlled variables were the granular material feed rate and the aspirating air speed rate. The monitored variable was the charge imparted to a well-defined section of the duct and which is equal to the charge transferred to the particles passing through that section of the pneumatic transport system. An induction type sensor connected to an electrometer has been employed for the measurements. The data were processed by a virtual instrument developed in LabView. A commercial software package was employed for estimating the effects of the various factors and predicting the optimum operating conditions, which were then confirmed by a final experiment.  相似文献   
45.
Pintu K. Kundu 《Tetrahedron》2010,66(44):8562-8568
The β-aryl-β-silyl and β,β-disilyl propionates have been synthesized from cinnamates and β-silyl acrylates by a regiospecific reductive C-silylation using Mg/silyl chloride/DMF system at room temperature. These reductive C-silylation conditions have also been applied to δ-aryl substituted dienoates wherein silylation took place at the δ-position leading to the synthesis of single regioisomeric allylsilanes with very high stereoselectivity.  相似文献   
46.
Tissue equivalent (TE) lyoluminescence (LL) dosimetry requires practical amount of phosphor for dissolution, typically 5-30 mg. Pronounced mass quenching effect has been observed even in the region of 5 mg, in the cases of LL of lactose-monohydrate, d-glucose, d-mannose, raffinose, sucrose and 1-glutamine. Ordinary concentration-quenching is non-existent but yield per mg falls rapidly with increasing mass of the phosphor. The curves have been fitted with a self-absorption type formula. A well-recognised dose effect is present in quenching curves. The role of free radicals at high radiation doses has been discussed in the contribution of dose effect in quenching.  相似文献   
47.
48.
49.
A canonical planar beta-hairpin peptide, stereochemically reengineered into a semicircular bracelet type motif by L-to-D stereochemical inversion in two pairs of its cross-strand neighbor residues, displays protein like ordering including two-state behavior in H2O, which is unusual for a small peptide of this size.  相似文献   
50.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号